1. Field of the Invention
The present invention relates to an instant photo film pack for self-developing photo film units with a light-shielding cover sheet, and an instant camera. More particularly, the present invention relates to an instant photo film pack in which a light-shielding cover sheet can effectively operate for protection from ambient light without influence to advancing photo film units, and an instant camera.
2. Description Related to the Prior Art
JP-A 7-209814 discloses an instant photo film pack with which an instant camera is loaded. The instant photo film pack includes a light-tight pack body having a box shape and formed from hard plastic material, and accommodates a stack of plural self-developing photo film units of a mono-sheet type.
Each of the photo film units is constituted by an exposure portion, a developing solution pod and a trapping portion. The exposure portion includes a photosensitive layer having an exposure surface, a white diffusion/reflection layer, and an image receiving layer having a back surface. The developing solution pod is disposed in an advancing direction from the exposure portion, and contains developing solution. When the developing solution is spread between the photosensitive layer and the image receiving layer, then a latent image recorded in the photosensitive layer is transferred to the image receiving layer as a positive image through the diffusion/reflection layer. The image transferred to the image receiving layer becomes observable in the back surface reverse to the exposure surface. The trapping portion is disposed in a direction reverse to the advancing direction from the exposure portion, and traps and hardens a surplus part of the developing solution spread between the photosensitive layer and the image receiving layer.
There is an exposure opening formed in the instant photo film pack for introducing light from a photographic subject to the exposure portion of one of the photo film units when positioned in the instant camera. A light-shielding cover sheet is stacked on the first one of the photo film units and is placed to close the exposure opening for preventing entry of ambient light. When a claw member of the instant camera is driven for a first time, the claw member pushes a bottom of the light-shielding cover sheet, so that the light-shielding cover sheet is advanced and exited from an exit slit of the instant photo film pack. The exit slit is disposed in a wall directed crosswise to the front wall of the instant photo film pack having the exposure opening.
The light-shielding cover sheet, when exited from the instant photo film pack, is advanced to a position between spreader rollers incorporated in the instant camera. The spreader rollers rotate to cause the light-shielding cover sheet to exit from the instant camera through a camera exit slot formed on a top wall of the instant camera. Upon the exiting of the light-shielding cover sheet, a first one of the photo film units is set at the exposure opening.
At each time that one exposure is taken, one of the photo film units is pushed up toward the outside by the claw member. The photo film unit is nipped by the spreader rollers and advanced toward the camera exit slot. Then the spreader rollers spreads the developing solution to the whole of the exposure surface of the photo film unit for a developing operation. Then a succeeding one of the photo film units is pushed up and set directly behind the exposure opening.
It has been found that the developing solution can be adequately spread if each of the photo film units is deformed in its thickness direction to compress a space for flow of the developing solution in the thickness direction. Thus it is desired for the instant camera to have a structure for deforming each photo film unit in the thickness direction in the course of the advance. A spreading control member has been conceived, which is disposed between the exit slit of the instant photo film pack and the spreader rollers. Also, a passageway between the spreader rollers and the camera exit slot is constructed with an inclination.
The spreading control member is desired to be disposed so as to push the developing solution pod of the one photo film unit from the exit slit of the instant photo film pack in a direction from the back surface toward the exposure surface. Also, a passageway between the spreader rollers and the camera exit slot is desired to have an inclination for the purpose of keeping the exposure surface of the one photo film unit in greater contact with one of the spreader rollers closer to the exposure opening.
In the instant camera as described above, the light-shielding cover sheet is exited while deformed in the thickness direction. If the light-shielding cover sheet has a great thickness, the light-shielding cover sheet does not flex, or applies excessive load to a motor driving the spreader rollers in the instant camera. There arises a problem in a quick consumption of power of a battery in the instant camera as a power source. If the light-shielding cover sheet is provided with a reduced thickness on the other hand, load applied to the spreader rollers can be reduced, as the light-shielding cover sheet can be readily deformed in the thickness direction. But there occurs a considerable gap between the light-shielding cover sheet and the inside of the exit slit in the instant photo film pack during the passage of the exit slit. It is likely that a first one of the photo film units before being exposed may be exited together with the light-shielding cover sheet.
In the instant photo film pack, a cutout is formed, disposed between a bottom wall and the front wall having the exposure opening, and has an L-shape as viewed in section for entry of the claw member. It is known according to the prior art to use black light-shielding film for closing the cutout light-tightly. The black light-shielding film is attached to the bottom edge of the light-shielding cover sheet, and extended downwards from the light-shielding cover sheet. The extended portion closes the bottom part of the cutout. However, the light-shielding cover sheet is easily deformable in the thickness direction particularly if the light-shielding cover sheet has a small thickness. Upon the deformation of the light-shielding cover sheet, there occurs a gap between an inner surface of the instant photo film pack and an end of the light-shielding cover sheet as viewed in its width direction crosswise to the advancing direction. As the cutout is located laterally in the width direction of the instant photo film pack, the occurrence of the gap may cause entry of ambient light through an end of the cutout, to fog or expose the exposure surface of the photo film units accidentally.